This invention relates to a fluid brake actuating mechanism including a service brake chamber and a spring actuated auxiliary brake chamber and more particularly to an improved means for centering and guiding the spring and piston of the spring actuated auxiliary brake mechanism.
Modern trucks and other heavy duty vehicles are normally equipped with pneumatic braking systems which are operated from a main pneumatic pressure source. Since a failure of the main pneumatic pressure source will interrupt the normal operation of such braking systems, it is now conventional to provide a spring actuated auxiliary brake mechanism which will automatically apply the service brakes in the event of a loss of pressure in the main pneumatic pressure source.
Thus the brake actuating mechanism of such pneumatic braking systems conventionally comprise a service brake chamber including a piston and rod assembly together with an impervious flexible diaphragm arranged so that the application of pneumatic pressure to one side of the diaphragm will cause the piston and rod assembly to move in the braking direction. A light helical compression spring is also provided in the service brake chamber to return the piston and rod assembly in the non-braking direction on removal of the pneumatic pressure.
A spring actuated auxiliary brake chamber is normally provided in tandem with the service brake chamber and includes a piston and heavy duty helical compression spring assembly together with a flexible impervious diaphragm arranged so that the application of pneumatic pressure to one side of the diaphragm will move the piston to compress the helical compression spring. A brake actuating rod assembly is provided on the opposite side of the flexible impervious diaphragm from the piston and is adapted to project into the service brake chamber and bear against the opposite side of the flexible diaphragm therein from the piston and rod assembly thereof when the helical compression spring of the auxiliary brake chamber is extended. Thus in normal operation, pneumatic pressure from the main pneumatic pressure source is applied to the auxiliary brake chamber to cause the piston thereof to compress the heavy duty helical compression spring. A light helical compression spring is provided in the auxiliary brake chamber to hold the brake actuating rod thereof in contact with the flexible impervious diaphragm so that the brake actuating rod does not normally project into the service brake chamber. Upon failure of the main pneumatic pressure source the heavy duty helical compression spring of the auxiliary brake chamber will drive the brake actuating rod into the service brake chamber and against the flexible impervious diaphragm thereof forcing the piston and rod assembly of the service brake chamber to move in the brake actuating direction.
The rod of the piston and rod assembly of the service brake chamber provides for self-centering of such piston and rod assembly during operation. Similarly, the brake actuating rod of the auxiliary brake chamber is self-centering in operation. However, the piston of the auxiliary brake chamber is essentially floating within the auxiliary brake chamber under the influence of the forces exerted thereon by the heavy duty compression spring and the flexible impervious diaphragm. Thus, appropriate means must be provided for centering the piston of the auxiliary brake chamber in operation.
It is the basic object of this invention to provide an improved means for centering the piston of a spring actuated auxiliary brake mechanism in operation.
In the prior art, various means for centering the piston of a spring actuated brake chamber in operation have been proposed based on the use of elongated concentric rods and cylinders in various arrangements. However, such arrangements have tended to add to the axial length of the auxiliary brake chamber.
It is another object of this invention to provide an improved means for centering the piston of a spring actuated auxiliary brake chamber in operation while reducing the axial length requirements for such chamber toward minimum.
It has also been proposed in the prior art to form the housing or head of the auxiliary brake chamber as well as the piston thereof with interfitting cavities and protuberances in order to provide for the centering of such piston in operation. However, such structures have been difficult and expensive to fabricate and have a given operational life imposed by the characteristics of the material which can be so formed in view of the wear which results due to the contact of surfaces thereof under pressure in operation.
It is a further object of this invention to provide an improved auxiliary brake actuating chamber providing for the centering of the piston thereof in operation which is simple and inexpensive to fabricate and which will have increased life in operation.